Method to ask a dynamic component instance to recalc itself?

Developers Ruby API
6

Yes, true, you are correct.

(1) It still exists.
(2) It itself is poor practice, and could have been a class variable reference (implemented in a singleton manner.) It could have been exposed via a class constant or a class getter method.
(3) As I said above, It might not exist in future versions, if they re-implement it’s reference per (2).

So, you’ll need to do a object search and hold a local reference inside your module, to the same singleton object that $dc_observers is also referencing.

def recalc_dc(inst)
  return nil unless defined?(DCObservers)
  if inst.is_a?(Sketchup::ComponentInstance) &&
  inst.attribute_dictionary('dynamic_attributes')
    if @dc_observers.nil?
      ObjectSpace.each_object(DCObservers) {|o| break @dc_observers = o }
    end
    return nil unless @dc_observers.respond_to?(:get_latest_class)
    latest_dc_class = @dc_observers.get_latest_class
    return nil unless latest_dc_class.respond_to?(:redraw_with_undo)
    latest_dc_class.redraw_with_undo(inst)
  end
  nil # (there is no particular return value)
end

But, since the DC extension is Trimble’s extension, there is still no guarantee they’ll approve your extension.